Doors equipped with dead bolts generally have a finger- or hand-manipulatable inside knob, allowing a user of the lock to unlock the door from inside without recourse to a key. It is important to be able to do this both for general convenience and because in such an emergency as a fire it may be necessary for an occupant of a house or room to exit through a door in the midst of darkness, smoke, and confusion that prevents the ready finding and use of a key.
When a door having such a lock in it has sidelites generally adjacent to the lock or has a window lite in the door itself within reaching distance of the lock, an intruder can gain entrance through the door by breaking the glass, reaching inside, and opening the lock by manipulation of the interior knob. Such doors are no more secure than the window the provides access to the lock. If a door has a strong frame with relatively weak panels or the like, a portion of the door itself may be broken through to provide access from the outside to the knob.
The art is cognizant of various methods for attempting to secure a door lock against such an assault. Ferrer, U.S. Pat. No. 3,563,069, teaches the use of a box-like structure that completely covers the doorknob associated with the lock on the interior side of a door. The cover is padlocked, making the doorknob inaccessible to someone breaking through a sidelite. Crockett, U.S. Pat. No. 4,227,386 is another example of the use of a cover over a lock assembly to prevent access thereto. Ferrer requires the use of a key to open the protective cover as a necessary first step to unlocking the door. Consequently, the system of securing the lock in Ferrer is no more convenient to a user than the lock of Hennesey, U.S. Pat. No. 4,272,974 or Shipman, U.S. Pat. No. 3,964,281, both of which provide for conventional keyed cylinders on both sides of a door.
Push button locks are generally known in the art. Examples include Check, U.S. Pat. No. 3,099,150, and Hartman, U.S. Pat. No. 4,014,194. The push buttons in Hartman remain fixed relative to the door as they are used. In Check the buttons are mounted in a knob. When the push buttons are appropriately depressed, activating a complicated rachet system that releases the knob, the knob can be turned to withdraw a bolt. In either case, nothing in the design of these push button locks prevents their operation by a person who has broken a window lite in or beside the door and is manipulating the lock, having thrust his arm through the broken window lite. In addition, a combination must be known to open the locks, which are intended to substitute for a conventional keyed cylinder on the exterior side of a door.